1. Field of the Invention
The present invention relates to a Light-Emitting Diode (hereinafter referred to as an ‘LED’) lighting, and more particularly, to a power supply apparatus for an LED lighting and an LED lighting apparatus using the power supply apparatus.
2. Description of the Related Art
In recent lighting apparatuses, incandescent lights and fluorescent lights are being replaced with LEDs capable of being implemented to have a relatively longer lifespan, low consumption power, and high brightness as lighting lamps.
The lighting apparatus may include, for example, a security light and a streetlamp. An LED lighting apparatus that adopts an LED lighting is also developed as the security light or streetlamp and commercialized.
An example of a conventional LED lighting apparatus is disclosed in Korean Patent Registration No. 10-1164631. In this patent, a commercial AC power source supplies a power to LEDs through a Switching Mode Power Supply (SMPS) module and a driving circuit.
In general, an LED lighting apparatus is configured to supply a power to an LED by controlling the operation of a transformer in accordance with a flyback control method.
In order to drive the transformer in accordance with the flyback control method, an operating voltage needs to be stably supplied to a flyback control circuit.
The transformer does not operate in the initial state in which the supply of AC power is started. Accordingly, the flyback control circuit drives the transformer using an operating voltage according to a startup current.
When the transformer normally operates, the flyback control circuit receives the operating voltage from the auxiliary coil of the transformer.
The flyback control circuit may be differently designed depending on manufacturers, but can be designed to perform a stable operation in an environment in which an operating voltage of 14 V to 20 V is supplied.
Furthermore, an LED lighting apparatus may have a dimming function for controlling the brightness of an LED lighting.
The dimming function is to control the brightness of an LED lighting by controlling an electric current supplied to the LED lighting.
The dimming function may be designed so that an LED lighting is turned off when the duty of a control pulse is less than 10%. Furthermore, the dimming function may be implemented so that the brightness of an LED lighting is controlled when the duty of a control pulse varies between 10% and 100%.
The duty of the control pulse corresponds to the amount of current supplied to the LED lighting.
Accordingly, when an current that is less than 10% of a maximum driving current is supplied, the LED lighting is turned off because sufficient voltage for turning on the LED lighting is not formed. Furthermore, when an current between 10% and 100% of a maximum driving current is supplied, the LED lighting emits light with brightness corresponding to the amount of current.
A conventional LED lighting apparatus implemented to have a dimming function is problematic in that an operating voltage supplied to a flyback control circuit becomes unstable when the driving current of an LED lighting is decreased to a turn-off level.
More particularly, in the state in which the LED lighting is in a maximum driving current state, the LED lighting apparatus can supply an operating voltage having a stable level, such as 24 V, to the flyback control circuit through the auxiliary coil of a transformer.
If the brightness of the LED lighting is gradually decreased to a turn-off level by way of dimming control, however, the operating voltage supplied from the auxiliary coil of the transformer to the flyback control circuit is gradually decreased in proportion to a reduction of a driving current.
Furthermore, when the brightness of the LED lighting drops to a turn-off level, the operating voltage supplied from the auxiliary coil of the transformer to the flyback control circuit drops to an unstable level of 14 V or less.
That is, the conventional LED lighting apparatus is problematic in that the flyback control circuit unstably operates due to a low operating voltage because an operating voltage supplied from the auxiliary coil of the transformer to the flyback control circuit is excessively lowered when the brightness of the LED lighting is controlled in a turn-off level.
As described above, the conventional LED lighting apparatus is problematic in that the operation of the flyback control circuit becomes unstable when an LED lighting approaches a turn-off level in implementing a dimming function.